MADISON, Wis. (AP) â?? The Upper Midwest remains locked in the deep freeze, with bitter temperatures stretching into a fourth day across several states.

The cold snap arrived Saturday night as waves of Arctic air swept south from Canada, pushing temperatures to dangerous lows and leaving a section of the country well-versed in winter's pains reeling.

Authorities suspect exposure has played a role in at least four deaths so far.

"I am wearing a Snuggie under a top and another jacket over that," said Faye Whitbeck, president of the chamber of commerce in International Falls, Minn., a town near the Canadian border where the temperature was minus 30 on Tuesday morning. The so-called "Nation's Icebox" reached a balmy 3 below for a high. "I pulled out a coat that went right to my ankles this morning and I wore two scarves."

Among the coldest temperatures recorded Tuesday was 35 below at Crane Lake, Minn., a National Weather Service forecaster said early Wednesday.

The coldest location in the lower 48 states Monday was Embarrass, Minn., at 36 below. On Sunday it was Babbitt, Minn., at 29 below, according to the National Weather Service.

Forecasters said late Tuesday that overnight temperatures wouldn't get that low, but warned it was still frigid: Embarrass, Minn., was up to 15 below by late Tuesday night.

Nighttime temperatures round 10 degrees made it harder for Chicago firefighters to battle a warehouse blaze described by officials as one of the largest in recent years. The Chicago Sun-Times reported late Tuesday that more than 170 firefighters responded to the five-alarm blaze at an abandoned warehouse on the city's South Side that took nearly three hours to get under control.

The Northeast was also feeling the chill from Ohio to Maine.

In Connecticut, overnight temperatures were expected to range from 0 to 10 degrees over the next several days, and the wind chill could make it feel as cold as minus 15 degrees in some parts of the state. In Millinocket, Maine, residents awoke to temperatures of minus 9 degrees

The bitter conditions were expected to persist into the weekend in the Midwest through the eastern half of the U.S., said Shawn DeVinny, a National Weather Service meteorologist in suburban Minneapolis.

Ariana Laffey, a 30-year-old homeless woman, kept warm with a blanket, three pairs of pants and six shirts as she sat on a milk crate begging near Chicago's Willis Tower on Tuesday morning. She said she and her husband spent the night under a bridge, bundled up under a half-dozen blankets.

"We're just trying to make enough to get a warm room to sleep in tonight," Laffey said.

But in Sioux Falls, S.D., where winter temperatures are normally well below freezing, some homeless shelters had open beds. Shelter managers suspect people who needed a place to stay were already using the services before the temperatures reached more extreme lows. The first cold snap of the season was in early December. Overnight temperatures dropped to 9 below with the wind chill. In Vermillion, S.D., a water pipe break forced the evacuation of a dormitory at the University of South Dakota, with nearly 500 students offered hotel rooms.

In Michigan's Upper Peninsula, residents woke to a wind chill that made it feel like 35 below. The temperature in Madison, Wis., was a whopping 1 degree above just before midday Tuesday. For northern Illinois, it was the first time in almost two years that temperatures had dipped below zero.

The temperature in Detroit was a toasty 7 degrees with a 10 below wind chill around midday. City officials said they planned to extend hours at its two warming centers. A warming center run by St. Peter and Paul Jesuit Church downtown that usually sees 50 to 60 people on a typical winter day had taken in about 90 people Tuesday morning.

Police in Milwaukee, where the temperature was just 2 degrees at noon, checked under freeway overpasses to find the homeless and urge them to find a shelter. The United Way of Greater Milwaukee has donated $50,000 to two homeless shelters so they can open overflow centers.

"We're incredibly relieved," said Donna Rongholt-Migan, executive director of the Cathedral Center, a Milwaukee shelter that received $25,000. "I was walking my dog last night and I couldn't feel my legs just after walking around the block."

Schools across the region either started late or didn't open at all. Districts in Duluth, Minn., and Ashland, Bayfield, Hurley, Washburn and Superior in far northern Wisconsin closed amid warnings that the wicked wind chills could freeze exposed flesh within a minute.

"It's brutal," Courtney Thrall, a 21-year-old University of Wisconsin-Madison student, said as she waited for her bus, her fur-trimmed parka hood pulled over her head.

On Sunday, a 70-year-old man was found frozen in his unheated home in Des Plaines, Ill. And in Green Bay, Wis., a 38-year-old man was found dead outside his home Monday morning. Authorities in both cases said the victims died of hypothermia and cold exposure, with alcohol a possible contributing factor.

A 77-year-old Illinois woman also was found dead near her car in southwestern Wisconsin on Saturday night, and a 61-year-old Minnesota man was pronounced dead at a hospital after he was found in a storage building Saturday morning.

The plunging temperatures made life plenty miserable for plumbers.

Workers in Madison had to repair at least four water main breaks since Sunday afternoon. Jim Gilchrist, a third-generation plumber in the Chicago suburb of Oak Park, said he received about five or six calls Tuesday from people with frozen water pipes in their homes. Few pipes had actually burst â?? yet.

"We'll probably get those calls later, as pipes begin thawing" and develop a split, Gilchrist said. "Today they just know they don't have water; tomorrow they will have water spraying."

At least two fires in southern Wisconsin were blamed on property owners using heaters or other means to thaw frozen pipes. In one case, a dairy barn was destroyed, and in the other, a mobile home was lost. No one was hurt.